The present invention relates to discontinuous fibers with a binder material coating which adheres solid particulate material to the fibers and to absorbent structures of such materials.
A number of techniques for applying binders to webs of fibers are known. For example, U.S. Pat. No. 4,600,462 of Watt describes a process in which an adhesive binder is sprayed onto one or both surfaces of an air laid cellulose fiber web. Submersion of the web in the adhesive binder is another method disclosed in this patent of applying the binder. Individual binder coated fibers for mixing with other fibers are not produced by this process. A hydrophile solution is also applied to the web. As another example, U.S. Pat. Nos. 4,425,126 and 4,129,132 of Butterworth, et al. describe a fibrous material formed by combining thermoplastic fibers and wood pulp, heat fusing the combined fibers, and thereafter depositing a binder on the heat fused web. Because the fibers are heat fused prior to adding the binder, individual binder coated fibers for mixing with other fibers are not produced by this process.
U.S. Pat. No. 4,584,357 of Harding discloses a latex treated cationic cellulose product and method for its manufacture. In the Harding approach, cationized cellulose is treated in an aqueous suspension with an anionic polymer emulsion of from 0.1 to 30 percent on a dry weight basis. The patent mentions that the resulting resin treated products can be prepared in sheet form, as loose fibers or in another form. The approach of the Harding patent is limited to cationic fibers. Also, the fiber coating applied as described in the Harding patent had a tendency to flake off or separate from the fibers. Moreover, because the Harding approach uses a wet process, the lumen of the cellulose fibers is penetrated by the polymer emulsion. Since the binder on the surface of the fibers contributes principally to the desired characteristics of the fiber, any polymer that penetrates the lumen of the fiber adds little to these desired characteristics.
U.S. Pat. No. 4,469,746 of Weisman, et al. discloses fibrous webs comprised of fibers coated with a continuous film of silica. The fibers are understood to be dispersed in a charged silica aquasol to accomplish the coating. Because silica is an inorganic material, the silica does not contribute to subsequent bonding of fibers. In addition, because Weisman, et al. discloses a wet process, the silica will tend to penetrate the lumen of cellulose fibers in the event such fibers are being treated in accordance with this patent.
U.S. patent application Ser. No. 067,669, filed Jun. 26, 1987, and entitled "Treated Wood Fiber Having Hydrophobic and Oleophilic Properties" by Jewell, et al., mentions an approach of treating fiberized wood with surfactant material to penetrate the surface of the wood fibers. In this approach, fiberized wood at the outlet of a first fiberizing machine passes through an orifice into a blow line. At the outlet of the fiberizing machine, liquid surfactant is injected into the line. At the point of addition of the surfactant, the fiber is still wet as it has been carried by steam through the fiberizing machine. Surfactants are not suitable for use in subsequent bonding of the fibers. The jewell, et al. patent application also describes a process in which fibers are treated with a copolymer latex, such as a combination of a paraffin wax emulsion and a styrene butadiene copolymer latex. The patent describes a suitable treating process as involving the blending of the aqueous latex emulsion with wood fiber in a typical mechanical wood fiber blender. This approach tends to produce fibers which are bound together by the latex.
U.S. Pat. No. 2,757,150 of Heritage mentions a fiber treatment approach in which fibers are carried by steam under pressure and in which a thermoset resin is introduced into the fiber stream. Other materials (i.e. rosin and wax) are mentioned as being simultaneously introduced into the fiber stream. The patent indicates that such materials penetrate the surface of the fibers. This patent mentions the individualization of these treated fibers. A relatively low concentration of the thermoset resin (i.e. two percent by weight phenol formaldehyde) is specifically described in this patent. At such low concentrations, the resin is in discontinuous random non-interconnected areas (blobs or globules) on the fibers. These treated fibers are typically used in hardboard. In current hardboard resin products produced using the approach of the Heritage patent and known to the inventors, a phenolic resin concentration of from a maximum of five to six percent by weight is used. Even at these concentrations, the resin forms random non-interconnected globules on the fibers. As a result, the uncoated resin free areas of the fibers lack the capacity to bond in comparison to the areas of the fibers covered by the resin. In addition, the untreated surface areas of the fibers may lack desired characteristics of the resin covered areas of the fibers. For example, these uncoated areas may cause the fibers to be more water absorbent than if the entire fiber was coated.
U.S. Pat. No. 4,006,887 of Engels describes a process for treating wood fibers in which the fibers are supported as an annular loose fluidized bed in a mixer which delivers glue by way of shaft mounted mixing rods to the fibers. The patent mentions that radial air vortices are established with the mixer inlet and outlet funnels being connected to an air transport pipe. The patent describes the resulting product as homogenous lump free uniformly coated wood fibers. The patent mentions that the coating of fibers is useful in the manufacture of wood fiber panels. The glue used in the Engels patent and the percentage of the glue that is used is not discussed.
The background portion of the Engels patent describes German Auslegeschrift 1,048,013 as disclosing an impeller or agitator mixer for the coating of wood chips with dusty components. Glue is described as being sprayed through nozzles into a mixing container. An air stream is described as being blown axially through the mixing container in order to reduce the residence time of dusty chip particles to reduce excessive coating of such dusty particles. Also, German Offenlegunge 1,632,450 is mentioned by Engels as disclosing wood chips agitated in an air stream in a mixing tube in which glue spray nozzles are mounted.
Heretofore, synthetic bicomponent fibers have been formed by extruding two materials in air in side-by-side strands which are connected together along their length. Such bicomponent fibers have also been formed with one material being extruded as a concentric sheath surrounding the other material. These extruded strands are then chopped or broken into discontinuous fibers. Although synthetic bicomponent fibers provide good structural efficiency, they are very expensive in comparison to natural fibers, and, therefore, their use is limited.
U. S. Pat. No. 4,261,943 of McCorsley, III describes the extrusion of filaments and the application of a solution of a nonsolvent liquid to the filaments. In this application process, the filaments are passed through a chamber having a nonsolvent vapor laden atmosphere, i.e. a fog of minute particles of nonsolvent. Spraying of the nonsolvent liquid onto the filaments is also mentioned. The approach of the McCorsley, III patent is not understood to apply to discontinuous fibers.
U.S. Pat. No. 4,010,308 of Wiczer describes foamed porous coated fibers. Fibers, described as organic or inorganic fibers of any character, are described as being coated with a foamable plastic material. Thermoplastic and thermosetting coatings are mentioned. In several examples, the coated fibers are made by passing continuous extruded filaments through a first bath of a ten percent polystyrene solution on toluene, evaporating the solvent, and passing the polystyrene coated fiber through a second bath containing a blowing agent, such as liquid n-pentane. The treated filaments are then heated to foam the coating. Rolls are used to rub solid particles into the porous surface of the foam coating. Fireproofing agents, lubricants such as graphite, pigments, and insecticides are among the examples of solid materials mentioned as suitable for rubbing into the coating. In another example, short lengths of cotton linters are described as being wet with a ten percent solution of a copolymer of polystyrene and acrylonitrile in about equal proportions dissolved in benzene. The solvent is evaporated in an air stream and the resulting coated cotton fiber is dipped in mixed pentanes. The product is then stirred in boiling water to cause foaming. Following foaming, the product is centrifugally dried and again dried in an air stream. The fiber is then mixed with a dry powder to fill the pores in the foamed coating with the powder. The placement of this fiber product in a container and heating the product to cause the adherence of the fiber surface contact points is also mentioned. The Wiczer patent appears to use a solution dipping approach as a means of applying the coating to the fibers.
U.S. Pat. No. 4,160,059 of Samejima describes a process in which a natural cellulose fiber (such as wood pulp fiber) is shredded and blended in air with a heat-fusible fiber. The blend is fed to a disintegrator to form supporting fibers to which an absorptive material is added. Heated air is applied to the resulting web to heat the web to a temperature above the melting point of the heat-fusible fiber to form bonds between the supporting fibers and absorptive material by heat fusion. Activated carbon black, Japanese acid clay, active alumina, and diatomaceous earth are mentioned as representative absorptive materials. Other powders, including super absorbents, are also mentioned as being bonded in place in this manner. The background portion of this particular patent also mentions a process in which wood pulp is disintegrated by a dry process, blended with active carbon black, and the blend spread on a wire screen. A binding material such as latex, starch and the like can also be sprayed on both surfaces of the web. With this latter approach, the active surface of the absorptive material is covered with a thin film of the binding material. Thus, under the Samejima approach, heat fusion is used to bind the particles to the fibers. As a result, a bound fiber web, as opposed to individualized fibers, is formed with the particles heat fused to the fibers. In U.S. Pat. No. 4,429,001 of Kolpin et al., melt-blown fibers are prepared by extruding liquid fiber-forming materials into a high-velocity gaseous stream. The stream of fibers is collected on a screen disposed in the stream with the fibers being collected as an entangled coherent mass. Absorbent particles are introduced into the stream of fibers at the point where the fibers are solidified sufficiently that the fibers will form only a point contact with the particles. The patent mentions that the particles can also be mixed with the fibers under conditions that will produce an area of contact with the particles. The introduction of other fibers besides melt-blown fibers into the resulting sheet product is also mentioned. The patent mentions that surfactants in powder form can be mixed with the sorbent particles used in forming the web or surfactants in liquid form can be sprayed onto the web after it is formed.
Finally, U.S. Pat. No. 4,392,908 of Dehnel describes a process for forming a thermoplastic adhesive resin on a surface of water soluble particles. The coated particles in a dry state are heated and pressed to bond them to a dry substrate (i.e. cellulose fluff). Mixing of absorbent particles with an aqueous latex, spraying resin onto the particles, and mixing the particles in a slurry are mentioned as approaches for coating the particles. Milling of the particles after coating with thermoplastic is mentioned as usually being necessary to produce free flowing particles. Thus, the Dehnel patent illustrates another approach for heat fusing particles to fibers.
Although prior art approaches are known, a need exists for improved discontinuous fibers with a binder material and with adhered particles.